The present invention relates to improvements in reversible heat pumps that operate in heating and cooling modes. The invention is particularly directed to heat pumps wherein there is a significant disparity in the refrigerant handling capacities of the heat exchangers in such heat pumps.
Reversible heat pump systems typically include a refrigerant loop with at least two heat exchangers. It is desirable to sometimes select different types of heat exchangers having considerably different capacities for handling the refrigerant in this loop. For example one might wish to use a brazed plate heat exchanger in combination with a more traditional coil heat exchanger in a reversible heat pump system.
The brazed plate heat exchanger typically comprises a series of brazed plates having channels formed therein for carrying the refrigerant. The brazed plates also have channels formed therein for carrying a heat exchange medium which is either heated or cooled by the refrigerant depending on whether the refrigerant is absorbing or giving up heat. These channels do not however provide the same refrigerant handling capacity as a typical coil heat exchanger that may be the preferred second heat exchanger in the reversible heat pump.
The channels of the brazed plate heat exchanger also cannot tolerate a significant build up of condensed refrigerant if this heat exchanger is to operate as a condenser during the heating mode when relatively hot refrigerant flowing through the channels of the heat exchanger is condensing and giving up heat. In this regard, any significant build up of condensed refrigerant in the heat exchanger will result in an increase in discharge pressure.
The above need to assure that the refrigerant is not appreciably condensed to liquid form in the smaller capacity brazed plate heat exchanger will however pose a separate problem for the downstream thermal expansion valve. In this regard, the downstream thermal expansion valve works best when the refrigerant is fed to this valve in liquid form free from bubbles.
It is an object of the invention to provide a heat pump system with a refrigerant loop that relieves a low capacity heat exchanger of any significant build up of condensed liquid refrigerant when operating as a condenser during the heating mode.
It is another object of the invention to provide a heat pump system with a refrigerant loop that assures that the refrigerant is appropriately subcooled before being applied to the thermal expansion valve.
The above and other objects are achieved by providing a receiver that receives refrigerant from a low refrigerant handling capacity heat exchanger when operating as a condenser in a reversible heat pump system during the heating mode. The receiver includes a subcooling device. The subcooling device takes refrigerant emitted from the suction outlet of the second heat exchanger operating as an evaporator and circulates the low pressure refrigerant back through the receiver containing the high pressure refrigerant from the low capacity heat exchanger operating as a condenser. The high-pressure refrigerant in the receiver is subcooled to a point where the liquid refrigerant can be provided to the thermal expansion valve without concern for the refrigerant being in other than complete liquid form.
The receiver containing the refrigerant is sized so as to accommodate the volume of excess refrigerant that will likely be present in the reversible heat pump during the heating mode. The size of the receiver is preferably somewhat larger than this volume of excess refrigerant.